Check if post contains a specific reusable block

has_reusable_block.php

function has_reusable_block( $block_name, $id = false ) {
    $id = (!$id) ? get_the_ID() : $id;
    if( $id ) {
        if ( has_block( 'block', $id ) ) {
            // Check reusable blocks
            $content = get_post_field( 'post_content', $id );
            $blocks = parse_blocks( $content );

            if ( ! is_array( $blocks ) || empty( $blocks ) ) {
                return false;
            }

            foreach ( $blocks as $block ) {
                if ( $block['blockName'] === 'core/block' && ! empty( $block['attrs']['ref'] ) ) {
                    if( has_block( $block_name, $block['attrs']['ref'] ) ){
                       return true;
                    }
                }
            }
        }
    }

    return false;
}